Location of a linear epitope recognized by monoclonal antibody S16 on the hemagglutinin-esterase glycoprotein of influenza C virus

We reported previously that monoclonal antibody S16, which had been raised against the hemagglutinin-esterase (HE) glycoprotein of influenza C/Ann Arb or/1/50 (AA/50) virus, recognizes a linear epitope present on the HE molecu les of all influenza C viruses examined except for viruses belonging to a l ineage represented by Aichi/1/81 (AI/81). Comparison of the deduced amino a cid sequence of HE between viruses on the AI/81-related lineage and those o n the others suggests that the epitope recognized by S16 is located in a re gion containing amino acid residue 403 and that a change from Glu to Lys at this position causes the loss of reactivity with the antibody. To prove it , the wild type (WT) HEs of AA/50 and AI/81 as well as their mutants with a n amino acid substitution at residue 403 were expressed in CV-1 cells from the recombinant simian virus 40 (SV40) and tested for reactivity with S16 b y immunoprecipitation, The results showed that the AA/50 virus WT and AI/81 virus mutant HEs (both having Glu at residue 403) were reactive with S16 w hereas the AI/81 virus WT and AA/50 virus mutant HEs (both having Lys at re sidue 403) were not. Furthermore, we examined the reactivity of S16 with tw o synthetic peptides (corresponding to residues 397-409) that possess Glu a nd Lys at position 403, respectively, by enzyme-linked immunosorbent assays . The results demonstrated that the former peptide but not the latter was r eactive with S16. These observations support strongly the notion described above. During this study it was also found that S16 cross-reacts with large T antigen of SV40. (C) 1999 Elsevier Science B.V. All rights reserved.